Field
The invention relates to a coupling device for coupling a bone anchor to a rod, and further relates to a bone anchoring device including such a coupling device. The coupling device includes a receiving part with a channel for receiving a rod and an accommodation space for pivotably holding a head of the bone anchor. The head can be locked at an angle by applying pressure onto it via a pressure member. The pressure member has a deformable portion. First, load is applied with a locking member to the pressure member to deform the deformable portion to lock the head. Thereafter, the locking member comes into contact with the rod and locks the rod. The coupling device permits insertion of the bone anchor from a bottom end of the receiving part, thus forming a modular polyaxial bone anchoring device that allows locking of the head and the rod in a sequential manner using a tool with a single drive portion that engages the locking member.
Description of Related Art
US 2013/0345761 A1 describes a polyaxial bone anchoring device including a bone anchoring element with a shank and a head in a receiving part pivotably coupled to the shank and having a channel for receiving a rod. A pressure member is arranged in the receiving part and is configured to exert pressure onto the head to lock the head in the receiving part. The pressure member has a deformable portion. Load applied to the pressure member by a locking member clamps the head, and thereafter the locking member contacts the pressure member such that the deformable portion is deformed and the locking member comes into contact with the rod and clamps the rod.